Description: Sal measures several angles with a protractor. Created by Sal Khan. And so the trick here is you would actually measure it the way you would measure any angle using an actual physical protractor. You'd want to put the center of the protractor right at the vertex of where the two lines intersect. I'm just using my regular web browser, if you look at the angle here, you see that the other line goes to 130 degrees.*Teacher Advisor is 100% free.